Electricity meter

[1] The earliest commercial uses of electric energy, in the 1880s, had easily predictable usage; billing was based on the number of lamps or motors installed in a building.

Shallenberger fell ill and was unable to refine his initial large and heavy design, although he did also develop a polyphase version.

For example, electronic loads such as computer power supplies draw their current at the voltage peak to fill their internal storage elements.

This flattening causes odd harmonics which are not permissible if they exceed specific limits, as they are not only wasteful, but may interfere with the operation of other equipment.

Electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) to give energy used (in joules, kilowatt-hours etc.).

The voltage coil consumes a small and relatively constant amount of power, typically around 2 watts which is not registered on the meter.

A permanent magnet acts as an eddy current brake, exerting an opposing force proportional to the speed of rotation of the disc.

The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power or rate of energy usage.

The disc drives a register mechanism which counts revolutions, much like the odometer in a car, in order to render a measurement of the total energy used.

The processing and communication section has the responsibility of calculating the various derived quantities from the digital values generated by the metering engine.

On a modern meter most if not all of this will be implemented inside the microprocessor, such as the RTC, LCD controller, temperature sensor, memory and analog to digital converters.

In some multi-unit buildings, a similar protocol is used, but in a wired bus using a serial current loop to connect all the meters to a single plug.

Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less.

[19][20] A study using a consumer-readable meter in 500 Ontario homes by Hydro One showed an average 6.5% drop in total electricity use when compared with a similarly sized control group.

Low cost generation capacity (baseload) such as nuclear can take many hours to start, meaning a surplus in times of low demand, whereas high cost but flexible generating capacity (such as gas turbines) must be kept available to respond at a moment's notice (spinning reserve) to peak demand, perhaps being used for a few minutes per day, which is very expensive.

Domestic variable-rate meters generally permit two to three tariffs ("peak", "off-peak" and "shoulder") and in such installations a simple electromechanical time switch may be used.

[citation needed] Radio-activated switching is common in the UK, with a nightly data signal sent within the longwave carrier of BBC Radio 4, 198 kHz.

[26] Most meters using Economy 7 switch the entire electricity supply to the cheaper rate during the 7 hour night time period, not just the storage heater circuit.

In South Africa, Sudan and Northern Ireland prepaid meters are recharged by entering a unique, encoded twenty digit number using a keypad.

TOD metering normally splits rates into an arrangement of multiple segments including on-peak, off-peak, mid-peak or shoulder, and critical peak.

Possible locations include on a utility pole serving the property, in a street-side cabinet (meter box) or inside the premises adjacent to the consumer unit / distribution board.

In the United States, Canada, and parts of Central and South America similar customers are normally served by three-wire single phase.

Additionally, three-wire customers normally have neutral wired to the zero side of the generator's windings, which gives earthing that can be easily measured to be safe.

The most common schemes seem to combine an existing national standard for data (e.g. ANSI C12.19 or IEC 62056) operating via the Internet Protocol with a small circuit board for powerline communication, or a digital radio for a mobile phone network, or an ISM band.

For the United Kingdom, any installed electricity meter is required to accurately record the consumed energy, but it is permitted to under-read by 3.5%, or over-read by 2.5%.

A refund of electricity paid for, but not consumed (but not vice versa) will only be made if the laboratory is able to estimate how long the meter has been misregistering.

Some combinations of capacitive and inductive load can interact with the coils and mass of a rotor and cause reduced or reverse motion.

Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields, etc.

[39] Disconnecting a meter's neutral connector is unsafe because shorts can then pass through people or equipment rather than a metallic ground to the generator or earth.

The introduction of advanced meters in residential areas has produced additional privacy issues that may affect ordinary customers.